March Nature Almanac: Crane chorus inspires awe and tears

Thousands of greater sandhill cranes lift off from their island roosts at dawn along the North Platte River downstream from Oshkosh, Neb. (Courtesy/Stephen Jones)

Where to see migrating sandhill cranes:

Lillian Annette Rowe Audubon Sanctuary, Gibbon, Neb. Staff and volunteers lead trips to viewing blinds along the river each morning before dawn and each evening around sunset, March-early April. Pre-register at rowe.audubon.org.

North Platte River between Lake McConaughy and Oshkosh, Neb. Roadside pullouts and bridges offer the opportunity to see greater sandhill cranes feeding in fields during the day and gliding down to their island roosts at night.

Alamosa National Wildlife Refuge, San Luis Valley. Tens of thousands of greater sandhill cranes descend on this refuge in March. Details: fws.gov/alamosa

Roger Tory Peterson described the spring gathering of cranes along Nebraska's Platte River as "one of the 10 greatest wildlife spectacles in North America."

Seeing the cranes for the first time, Boulder resident Mary Balzer felt transformed.

"When I heard the calls of the thousands of cranes descending to the river at dusk, it was a primal sound ... touching a place in my soul that could somehow remember all the eons of their migration."

Many observers break out in tears. Others say their lives are changed forever.

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Aldo Leopold referred to the voice of sandhill cranes as "the trumpet in the orchestra of evolution." Along the Platte River in early spring, the cranes' rattling, primeval chorus begins well before dawn and builds to a pulsating, echoing roar, evoking images of the time when birds like these flew over the dinosaurs.

In March and early April, more than a half million lesser and greater sandhill cranes converge on a 200-mile stretch of the Platte to rest and refuel before continuing their journey from the Gulf Coast and Mexico to nesting areas in the northern United States, Canada, Alaska and Siberia.

From the public viewing blinds at National Audubon's Rowe Sanctuary near Gibbon, Neb., visitors experience what Boulder's Jessica Sandler described as "cranes arriving in undulating waves as far as the eye can see, cooing softly to their mates and offspring, drifting down from the skies as if in parachutes."

Along the North Platte River west of Lake McConaughy, huge, trumpeting masses of greater sandhill cranes explode skyward from their island roosts each dawn. Throughout the day in nearby fields, pairs stretch out their wings to catch the breeze and perform their leaping, floating and bowing courtship dances.

Because sandhill cranes nest on the ground and must remain vigilant for predators while incubating eggs and raising chicks, they have little chance to forage during the breeding season. Therefore, their survival depends on the four to five weeks they spend along the Platte River.

Historically, the cranes feasted primarily on invertebrates found in wet meadows bordering the river. Today they supplement this diet with corn and other crops gleaned from neighboring fields. Roosting at night on islands in the river protects cranes from predators.

Flood and fire control, encroachment of deciduous trees and shrubs, and agricultural diversions have reduced the once mile-wide Platte River to a narrow channel where islands suitable for roosting have grown scarce. At the Rowe Sanctuary, biologists clear the remaining islands of shrubbery each year to enable the cranes to roost without fear of predator ambush.

Low water flows also threaten roosting areas. During drought years, coyotes and foxes can easily wade across the channel to the island roosts. Each spring, several dozen cranes die after crashing into power lines close to the river.

Despite these threats, numbers of migrating sandhill cranes have increased gradually during recent years, thanks to tireless efforts of biologists and volunteers to protect and improve roosting habitat. Global warming and subsequent dewatering of the Platte River, along with invasion of the river's islands by weeds and trees, could reverse these gains.

For those of us who journey to Nebraska each spring to revel in the gathering of cranes, their potential loss seems inconceivable. While standing amid the swirling flocks one evening, Mary Balzer said, "I felt a great sadness, that humans are making it so difficult for these animals to survive. I cried for them and for us."

Stephen Jones and Ruth Carol Cushman are authors of "Wild Boulder County" and "The North American Prairie."

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